<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        body {
            margin: 0;
            font-size: 20px;
            text-align: center;
        }

        .wrap {
            width: 900px;
            margin: 0 auto;
        }

        #header {
            height: 100px;
            background-color: #6cf;
        }

        #main {
            height: 500px;
            background: #ccffff;
        }

        #footer{
            height: 80px;
            background: #99ccff;
        }
    </style>
</head>
<body>
<header id="header" class="wrap">header</header>
<section id="main" class="wrap">main</section>
<footer id="footer" class="wrap">footer</footer>
</body>
</html>